could u pls let me know how to find the limit easily and which equation will use for those? and pls explain in detail, not only write the steps

\f5. Use polar coordinates to find the limit lim 12cos(x- + y-). [Hint: Let x = rcoso and x = rsino, and note (x, y) - (0, 0) that (x, y) - (0, 0) implies r = 0.]6. Find the limit lim f(x + Ax, y) - f(x, ) Ax - 0 Ax for the function f(x, y) = 4x2- 5y. Oz 7. Find the partial derivative for the function z = cos(x3 + 12). 8. For f(x, y) = sin(27xy), evaluate fy at the point |2